Complex life on Earth is older than we think

Cosmos Magazine


Cosmos is a quarterly science magazine. We aim to inspire curiosity in ‘The Science of Everything’ and make the world of science accessible to everyone.

By Cosmos

A chance encounter in remote Australia, and years of painstaking analysis has pushed back evidence for the start of complex life on the planet by 750 million years.

Dr Erica Barlow, a geobiologist from the University of New South Wales (UNSW), uncovered the new understanding of how life formed on the planet, by analysing a rock she had placed on her desk.

Barlow found the rock while on an undergraduate field trip in the Western Australian outback, a decade ago.

She was studying stromatolites as part of her Honours research project, and spent her days in the Pilbara mapping the area and analysing the rock structures.

Barlow was walking back to the campsite when a small, shiny black rock reflecting the sunlight caught her eye. It stood out to her in the otherwise red landscape, so she picked it up as a memento of her trip.

The pet rock sat on Barlow’s desk at the Australian Centre for Astrobiology for several months while she worked on her stromatolite project.

Her supervisor at UNSW, Adjunct Professor Martin Van Kranendonk, saw the rock – known as black chert – and encouraged her to look for microfossils inside.

What she saw shook her.

“I was just amazed,” she says. “I’d never seen anything like it before.”

Most microfossils are shaped like long filaments, but this fossil was round.

“There was nothing else like the microfossil I found, in the geological record,” says Barlow.

“It was an entirely new type of life.”

4 erica barlow at the campsite credit josh jesse edit
Erica Barlow in the field (Image Josh Jesse)

Independent dating of the rock layers surrounding the embedded black chert suggest the microfossils are about 2.4 billion years old.

This age estimate coincides with the ‘Great Oxidation Event’: a volatile tipping-point in Earth’s history when oxygen levels on the planet’s surface dramatically and irreversibly increased. 

Barlow says the sharp, one-time rise of oxygen has been theoretically linked to the development of all complex life on Earth, but there has been nothing in the fossil record to demonstrate this theory – until now. 

“We’ve shown the first direct fossil evidence linking the changing environment during the Great Oxidation Event with an increase in the complexity of life,” says Barlow.

“It shows a step up in the organisation of life at this time.”

The sudden increase in oxygen during the Great Oxidation Event would forever change this landscape. The event is sometimes referred to as the ‘Oxygen Catastrophe’ – catastrophic for many life forms of the time, which needed low-oxygen environments to survive.  

“This would have created a lot of turmoil for life at the time,” says Barlow. 

This is an extract from an article on the UNSW Newsroom.

Read more on complex life at Australian fossil sites

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